The layout of struct coap_address_t is platform-dependent. This
change introduces getter/setter functions to retrieve and modify
the port component:
uint16_t coap_address_get_port(const coap_address_t *addr)
void coap_address_set_port(coap_address_t *addr, uint16_t port)
The respective port is given in host byte order and will be
converted to/from network byte order automatically.